DE10346674A1 - Motor vehicle electrohydraulic, brake-by-wire braking system has a mechanism for changing the operating characteristic of the brake pedal by changing the volume of a hydraulic chamber using a solenoid valve - Google Patents

Abstract

The electrohydraulic braking system for a vehicle brake-by-wire system has a device (29-31, 45) that permits changing of a preset brake pedal operating characteristic by solenoid valve controlled changing of a hydraulic fluid volume in a hydraulic chamber (21) that cooperates with the pedal.

Description

The invention relates to a brake system for motor vehicles, which can be operated in a "brake-by-wire" mode, with:
a master cylinder, are connectable to the wheel brake cylinder,
a first piston coupled to a brake pedal,
a second piston that actuates the master cylinder,
a third piston operable by the first piston, wherein at least one brake pedal characteristic simulation device is provided between the first and third pistons, which in the by-wire mode provides the driver with a comfortable pedal feel,
and all three pistons and the brake pedal characteristic simulation device are arranged in a housing,
with a hydraulic pressure source and a valve device for reducing the pressure of the pressure source to a value with which the second piston can be acted upon,
wherein the second and third pistons are separated from each other by a gap such that the third piston is acted upon by the pressure acting on the second piston in the direction opposite to the direction of application of the second piston.

In Automotive technology find brake-by-wire braking systems increasingly widespread. In these brake systems, the brake can also without active action of the driver due to electronic signals "foreign" operated. This electronic Signals can for example, an electronic stability program ESP or a distance control system ACC are issued. Does it come to a superposition of such foreign operation with a driver's confirmation, so feels the driver of the motor vehicle has a reaction in the brake pedal in Form of a deviation from the usual pedal characteristic. This Retroactive effect on the one hand, the brake pedal can be unfamiliar to the driver and be uncomfortable, leaving the driver in a critical situation of road traffic the brake pedal is not pressed as hard as it is in this situation would be necessary since he is by the foreign operation the brake caused interference the brake pedal characteristic is irritated, on the other hand receives the driver for ABS and ESP control activities a haptic feedback by Brake pedal vibrations. Desirable would be a full Avoidance of interference the brake pedal characteristic and compared to the conventional state Brake systems reduced, electronically controlled pedal vibrations.

The EP 1 078 833 A1 describes an electro-hydraulic brake system of the type mentioned. Due to the special arrangement of the pistons decoupling of the brake pedal is achieved by said hydraulic components, so that the above-mentioned reaction effect can be largely eliminated. As less advantageous is to be regarded in the known brake system the fact that the brake pedal characteristic in the "brake-by-wire" mode by the properties of the brake pedal characteristic simulation device forming passive elastic and damping elements is fixed and no haptic feedback of the brake system to the driver's foot allowed.

It is therefore an object of the present invention, a brake system of specify the type mentioned above, in which an active intervention in the brake pedal characteristic simulation device in the sense of above haptic feedback is possible. Furthermore the brake system should have a simple structure and inexpensive to produce be.

These Task is inventively characterized solved, in that a device is provided which is controlled by a valve of the pressure medium volume in the hydraulic chamber one of by the brake pedal characteristic simulation device predetermined Brake pedal characteristic deviating, electronically controllable Pedal behavior allows. The device is preferably provided by the electrical control and control unit controllable.

to Concretization of the inventive concept is in an advantageous Further development of the subject invention provided that the electrical controllable device by a first connection between the hydraulic chamber and a pressureless fluid reservoir inserted, electromagnetically switchable first 2/2-way valve, one in a second connection between the hydraulic chamber and the pressureless fluid reservoir inserted, electromagnetically switchable second 2/2-way valve, as well as an electromagnetic switchable third 2/2-way valve is formed, which in one leading to the pressure source Line inserted is.

advantageous Further developments of the subject invention are in the dependent claims 4 to 15 listed.

in the The following is an example of an embodiment of the invention with reference to the attached schematic drawings explained in more detail. It demonstrate:

1 the structure of the brake system according to the invention according to a first embodiment in the resting state,

2 an alternative embodiment of a brake pedal characteristic simulation device, in the brake system according to 1 Can be used.

1 shows the brake system according to the invention in the idle state. The brake system has a brake pedal 3 on, that over an operating rod 38 with a first piston 2 is firmly connected. The brake pedal travel can be achieved by means of a displacement sensor 17 be recorded. The first piston 2 is in a third piston 5 arranged, between the first and the third piston, a hydraulic chamber 21 is arranged in the elastic elements 6 . 7 are arranged on the first and third pistons exert forces and together with damping and / or friction elements, not shown, form a brake pedal characteristic simulation means which simulator force between the first ( 2 ) and the third piston 5 causes.

Furthermore, a second piston 4 provided, the master cylinder 1 is assigned and allows pressure build-up therein. The master cylinder 1 is about an only schematically indicated electro-hydraulic control unit 28 an anti-lock control system (ABS) connected to not shown wheel brakes of the vehicle.

The first ( 2 ), the second ( 4 ) and the third piston 5 are in a housing 8th accommodated. Between the third piston 5 and the second piston 4 there is a gap 11 , which is filled with pressure medium.

When the brake pedal is pressed 3 the driver moves the first piston 2 against the simulator force generated by the brake pedal characteristic simulation means. The passive elastic (contained in the brake pedal characteristic simulation device 6 . 7 ) and rubbing or damping elements are designed to give the driver the brake feel that corresponds to a common brake pedal characteristic. This means that at low brake pedal travel, the pedal force first jumps to an initial value, initially increases slowly with further pedal travel and then increases disproportionately with a larger brake pedal travel.

When the brake pedal is depressed, the pressure in the space becomes 11 in a hydraulically controlled operating mode by means of a first valve device so controlled that the third piston 5 in the immediate vicinity of a stop 35 in the case 8th and in a preferred "by-wire" mode of operation by means of a second valve means such that the third piston 5 in abutment with the stop 35 in the case 8th remains. The "by-wire" mode of operation includes both the driver triggered by a depression of the brake pedal, as well as autonomous, that is electronically controlled, initiated without the driver's intervention stunts and their overlays. In the former operating mode pedal movement and pedal force are largely decoupled in the second mode of operation of the operating state of the master cylinder 1 , Pressure pulsations in the master cylinder 1 , which occur in ABS and ESP control operations, unlike conventional brake systems can not access the brake pedal because of this decoupling.

In hydraulically controlled operating mode, pressing the brake pedal 3 and the associated construction of a simulator force the third piston 5 in the direction of the second piston 4 be moved, which already after a very small travel a valve device 10 is pressed. The valve device 10 is formed in the illustrated example as a hydromechanical booster valve, which is a valve body 13 comprising, by means of a spring 32 towards the second piston 4 is biased to and has two control edges, whose task will be explained in the following text. A hydraulic connection 12 allows applying to the gap 11 facing away from the end face of the valve body 13 with the in the space 11 controlled pressure. The valve body 13 acts together with an actuating element, which in the example shown as a on the third piston 5 molded radial projection 14 is trained. Moves the third piston 5 a little towards the second piston 4 , then follows the valve body 13 his movement until a connection between the space 11 and a hydraulic pressure source 9 will be produced. This connection is made by the fact that the right in the drawing control edge of the valve body 13 the flow path between one of the pressure source 9 leading hydraulic pressure line 23 or a branch of this branching line section 34 and one in the space 11 opening pressure medium channel 35 releases. The hydraulic pressure source 9 is preferably by a high-pressure accumulator 19 formed by a motor pump unit 20 is charged. The engine-pump unit 20 consists of an electric motor 26 and a hydraulic pump 27 , The suction side of a pressureless pressure medium vorvor storage container 22 is connected while its pressure side via the previously mentioned line 23 with the high-pressure accumulator 19 communicates. In the line 23 is one to high pressure storage 19 opening check valve 24 inserted, wherein a pressure sensor 39 the monitoring of the state of charge of the high-pressure accumulator 19 allows. The high-pressure accumulator 19 supports the pump 27 especially in those cases where pressure has to be built up in a short time, for example in a fast emergency braking, the pump 27 can not deploy immediately due to their inertia. By means of the connection between the high-pressure accumulator 19 and the gap 11 this is pressurized, whereby the second piston 4 in the master cylinder 1 Pressure builds up and the third piston 5 in the direction of a stop 35 in the case 8th is pressed, to which he applied before pressing the brake. On to the high-pressure accumulator 19 connected valve 15 , A pressure build-up valve is closed in the de-energized state, while a in the pressure medium channel 34 inserted separating valve 16 , In the illustrated embodiment, an isolation valve, is opened in the de-energized state, so that the pump 27 or the high-pressure accumulator 19 the gap 11 can apply pressure via the connection explained above. A pressure sensor 18 can the in the space 11 capture the applied pressure. By energizing the isolation valve 16 may be a drainage of pressure fluid from the gap 11 over the valve device 10 be prevented while energizing the pressure build-up valve 15 the gap 11 Pressure medium can be supplied.

In the unactuated state of the brake pedal 3 becomes the first piston 2 over the elastic elements 6 and 7 against a stop 37 pressed in the third piston 5 is trained. The elastic elements 6 . 7 , which form the previously mentioned brake pedal characteristic simulation device, are in the example shown in one of the first ( 2 ) and third piston 5 limited hydraulic chamber 21 arranged, on the one hand with the pressure fluid reservoir 22 and on the other hand with the pressure source 9 or the high-pressure accumulator 19 is connectable. In the first connection 40 between the hydraulic chamber 21 and the pressure fluid reservoir 22 caused by a relative movement of the third piston 5 opposite the housing 8th can be shut off, is an electromagnetically actuated, preferably normally open (SO) 2/2-way valve 29 inserted, with the shut-off of the hydraulic chamber 21 This is done by the mouth of the third piston 5 trained connection section 40a one in the housing 8th immovable seal 41 overruns. In the second connection 42 between the hydraulic chamber 21 and the pressure fluid reservoir 22 in the direction of actuation of the pistons 2 . 5 behind the seal 41 to the connecting section 40a is connected, is a second electromagnetically actuated, preferably normally closed (SG) 2/2-way valve 30 inserted, at its input port at the same time another hydraulic line 43 connected to the pressure source 9 or the high-pressure accumulator 19 leads. In the line 43 are a third, electromagnetically actuated, preferably normally closed (SG) 2/2-way valve 31 , as well as to the high-pressure accumulator 19 closing check valve 44 inserted as well as another pressure sensor 32 connected, the determination of the in the hydraulic chamber 21 prevailing pressure serves. In addition, to the line 43 a second (auxiliary) high-pressure accumulator 33 be connected. The third 2/2-way valve 31 locks in its first switching position, the hydraulic line 43 while it is in its second switching position the function of a high-pressure accumulator 19 back blocking check valve met. The previously mentioned 2/2-way valves 29 . 30 , and 31 form an electrically controllable device, which in the mode "brake-by-wire" a change in the pressure medium volume in the hydraulic chamber 21 and allowing a pedal behavior deviating from the brake pedal characteristic predetermined by the brake pedal characteristic simulation means.

2 shows an alternative embodiment of the brake pedal characteristic simulation device, in which the elastic element or the compression spring 6 outside the hydraulic chamber 21 is arranged and thus remains "dry".

The brake system according to the invention described in connection with the drawing can of course be operated in other modes. Thus, in an operating mode characterized by a braking action independent of the driver's will, the operating pressure in the gap 11 controlled by driving the second valve means a continuously recalculated target pressure value. This can be done by energizing the isolation valve 16 the volume flow to the valve device 10 be prevented while the possibility of reverse flow from the first valve device 10 through the isolation valve 16 to build up pressure in the intermediate space 11 preserved. About the pressure build-up valve 15 can be adjusted electronically controlled, a higher actuation pressure than that, the hydromechanical booster valve, the valve device 10 would pretend. For electronically controlled pressure reduction is the energization of the isolation valve 16 temporarily suspended, so that pressure medium to the valve device 10 can drain, in this operating condition, a connection to the pressure fluid reservoir 22 manufactures. This connection is due to the fact that the left in the drawing control edge of the valve body 13 the flow path between the Pressure fluid channel 45 and one of the valve means 10 to the pressure medium reservoir 10 leading hydraulic connection 36 releases. This electronic brake pressure control has the advantage that its transmission behavior is freely selectable within the given by the technical data of high-pressure accumulator, pressure build-up and isolation valve dynamics. Therefore, a so-called Springerfunktion, ie jumping to a predetermined brake pressure value when tapping the brake pedal 3 , Brake Assist function, deceleration control, and autonomous braking, such as those required for ASR (Drive Slip Control), ESP (Electronic Stability Program), and ACC (Adaptive Cruise Control), are realized by software measures. For this purpose, the driver specification in the form of a brake pedal operation, which is detected by displacement, force or other sensors, converted by the electronic control unit not shown by applying appropriate algorithms in Radbremsdrücke using the electronically switchable valves in the power brake module and the downstream ABS hydraulics can be realized.

In the already mentioned preferred "brake-by-wire" operating mode, which is characterized by an external braking process initiated by the driver deceleration request, the space becomes 11 by a corresponding control of the valves 15 . 16 by means of the electronic control and regulating unit, not shown, in accordance with the signal of the path sensor detecting the driver's request 17 regulated a hydraulic pressure. This pressure is always such that it is sufficient to the third piston 5 at his stop 35 in housing 8th to keep. This results in a brake pedal characteristic ie a mathematical functions describable relationship between brake pedal force, brake pedal travel and brake pedal speed, in the operating state of the master cylinder 1 not received. The essential parameters of the brake pedal characteristic are the stiffnesses and biases of the elastic elements 6 and 7 , A haptic feedback on the driver's pedal can be achieved by an electronically controlled deviation from the predetermined by passive elements brake pedal characteristic. For this purpose, according to the invention by means of electrically controllable valves 29 . 30 . 31 the pressure medium volume in the hydraulic chamber 21 controlled, with the otherwise open hydraulic connection 40 between the hydraulic chamber 21 and the reservoir 22 is shut off. To terminate an operating phase of the brake system with different brake pedal characteristic is simply the connection 40 released again. The valve switching operations for superimposing the predetermined brake pedal characteristic (Force Feedback Pedal) are described in more detail in the following text.

To push back the brake pedal 3 first becomes the first connection 40 the hydraulic chamber 21 with the pressure medium reservoir 22 by switching the first 2/2-way valve 29 shut off. Then the chamber 21 by controlled opening of the third 2/2-way valve 31 subjected to a hydraulic pressure, whereby additional pressure medium in the chamber 21 flows and the pedal 3 is pushed back. By observing the pressure in the chamber 21 with the help of the pressure sensor 32 and the brake pedal movement by means of the displacement sensor 17 the driver's request can be detected despite the additional restoring force. For active degradation of the in the chamber 21 introduced additional pressure medium volume is the first 2/2-way valve 29 kept closed and the pressure fluid volume by opening the second 2/2-way valve 30 in the pressure medium reservoir 22 drained. By keeping the valve closed 29 becomes the previously mentioned seal 41 spared from the mouth of the connecting section 40a can be driven over. When no additional restoring force is required, after complete removal of the additional pressure medium volume, the second 2/2-way valve is used 30 the hydraulic chamber 21 by opening the first 2/2-way valve 29 switched back without pressure. This will follow the path of the brake pedal 3 again the predetermined passive brake pedal characteristic.

In a third operating mode, which is characterized by a failure of the electrical power supply or the so-called hydraulic fallback level, the electromagnetic valves remain 15 and 16 energized. This allows the valve device 10 , the hydromechanical booster valve, the operating pressure in the interspace 11 regulate and thus cause a brake booster. In this case, the pressure build-up by the interaction of the right in the drawing control edge of the valve body 13 with the line section 34 regulated, while the pressure reduction by the interaction of the left in the drawing control edge with the hydraulic line 36 is regulated. The hydraulic booster funktiorniert without electricity, as long as the high-pressure accumulator 19 can deliver under pressure pressure medium. There is a linear force gain, the gain factor of which is the ratio of the cross-sectional areas of the second piston 4 to third piston 5 is fixed.

In a fourth mode, due to the lack of hydraulic pressure in the accumulator 19 or the so-called mechanical fallback level is characterized, the brake system can be actuated purely mechanically, the third piston 5 moves under the action of a brake pedal 3 initiated actuating force from its stop 35 away and move the second piston 4 by a mechanical power transmission, so that the actuation of the master cylinder 1 done exclusively with muscle power. By taking place relative movement of the third piston 5 opposite the housing 8th there is a shut-off of the above-mentioned hydraulic chamber 21 By connecting the mouth of one to the hydraulic chamber 21 connected line 40 one in the housing 8th arranged, fixed seal 41 overruns. The shutoff becomes the function of the brake pedal characteristic simulation device 6 . 7 switched off, so that a direct power transmission from the first ( 2 ) on the third piston 5 takes place.

With Help of deviating from the specified brake pedal characteristic Pedal behavior can to the driver electronically controlled pedal vibrations haptic feedback be given to the operating state of the brake control system can this information about Frequency and intensity the vibration can be quantified. Furthermore, the driver through an electronically controlled, temporary pushing back the brake pedal a feedback given when an ABS or ESP control is performed. Preferably, these deliberate feedbacks are reduced in intensity designed as those in conventional Braking systems inherently unavoidable strong and often disturbing or irritating pedal feedback.

Claims (15)

Electrohydraulic brake system for motor vehicles, which can be activated in a "brake-by-wire" mode both by the driver and independently of the driver, with a master cylinder (FIG. 1 ), are connectable to the wheel brake cylinder, - a first piston ( 2 ), with a brake pedal ( 3 ), - a second piston ( 4 ), the master cylinder ( 1 ), - a third piston ( 5 ), from the first piston ( 2 ), whereby between the first ( 2 ) and the third piston ( 5 ) at least one brake pedal characteristic simulation device ( 6 . 7 ), which in the "brake-by-wire" mode gives the driver a comfortable pedal feel, between the first ( 2 ) and the third piston ( 5 ) one with the brake pedal characteristic simulation means ( 6 . 7 ) cooperating hydraulic chamber ( 21 ) is limited and all three pistons ( 2 . 4 . 5 ), as well as the brake pedal characteristic simulation device ( 6 . 7 ) in a housing ( 8th ) are arranged, - a controllable by means of an electronic control and regulation unit hydraulic pressure source ( 9 ), and - one by the third piston ( 5 ) operable valve device ( 10 ) for reducing the pressure of the pressure source ( 9 ) to a value with which the second piston ( 4 ) is acted upon, wherein the second (4) and the third piston ( 5 ) through a gap ( 11 ) are separated from each other so that the third. Piston ( 5 ) by the second piston ( 4 ) acting pressure in the loading direction of the second piston ( 4 ) opposite direction, characterized in that a device ( 29-31 . 45 ) provided by solenoid valve controlled change of the pressure medium volume in the hydraulic chamber ( 21 ) allows a different from the predetermined by the brake pedal characteristic simulation device brake pedal characteristic pedal behavior. Brake system according to claim 1, characterized in that the device ( 29-31 ) is electrically controlled by the electronic control unit. Brake system according to claim 2, characterized in that the electrically controllable device by a in a first connection ( 40 ) between the hydraulic chamber ( 21 ) and a pressureless pressure fluid reservoir ( 22 ), electromagnetically switchable first 2/2-way valve (29), one in a second connection ( 42 ) between the hydraulic chamber ( 21 ) and the unpressurised pressure fluid reservoir ( 22 ) inserted, electromagnetically switchable second 2/2-way valve ( 30 ), as well as an electromagnetically switchable third 2/2-way valve ( 31 ) formed in one to the pressure source ( 9 respectively. 19 ) leading line ( 43 ) is inserted. Brake system according to claim 2 or 3, characterized in that a pressure sensor ( 32 ) for the determination in the hydraulic chamber ( 21 ) prevailing pressure is provided. Brake system according to one of claims 2 to 4, characterized in that the first 2/2-way valve ( 29 ) is designed as a normally open (SO) valve, while the second 2/2-way valve ( 30 ) is designed as a normally closed (SG) valve. Brake system according to one of claims 2 to 5, characterized in that the third 2/2-way valve ( 31 ) is formed as a normally closed (SG) valve, which in its first switching position, the hydraulic line ( 43 ) and in its second switching position the function of a pressure source ( 9 respectively. 19 ) complies with closing check valve Brake system according to one of claims 1 to 6, characterized in that a sensor ( 39 ) for monitoring the state of charge of the high pressure accumulator ( 19 ) is provided, whose Ausgangssig nal the electronic control unit is supplied and in the housing ( 8th ) is integrated or positively connected with this. Brake system according to one of claims 1 to 7, characterized in that a pressure sensor ( 18 ) for detecting the in the space ( 11 ) is provided ruling pressure whose output signal is supplied to the electronic control unit and in the housing ( 8th ) is integrated or positively connected with this. Brake system according to one of the preceding claims, characterized in that to the master cylinder ( 1 ) an electro-hydraulic control unit ( 28 ) of an anti-lock control system (ABS) is connected. Brake system according to one of the preceding claims, characterized in that the brake pedal characteristic simulation device at least one elastic element ( 6 . 7 ) containing one of the relative paths between the first ( 2 ) and third piston ( 5 ) dependent "spring force" portion exerts the force applied by the brake pedal characteristic simulation means. Brake system according to claim 12, characterized in that the brake pedal characteristic simulation device contains at least one damping device, one of the relative speed between the first ( 2 ) and third piston ( 5 ) dependent "damping force" portion exerts the force applied by the brake pedal characteristic simulation means. Brake system according to claim 12 or 13, characterized in that the brake pedal characteristic simulation device ( 6 . 7 ) contains at least one of the components "steel spring, elastomer body and friction joint", which exert the force applied by the brake pedal characteristic simulation means. Brake system according to claim 14, characterized in that each of the components exerting the force applied by the brake pedal characteristic simulation means either outside ("dry") or inside ("wet") the hydraulic chamber ( 21 ) is arranged. Brake system according to one of the preceding claims 1 to 13 characterized in that the of the predetermined brake pedal characteristic deviant pedal behavior electronically controlled pedal vibrations includes. Brake system according to one of the preceding claims 1 to 13 characterized in that the of the predetermined brake pedal characteristic deviant pedal behavior an electronically controlled temporary pushing back of the Includes brake pedals.